Date: Fri, 19 Apr 2019 20:36:16 -0700 From: Mark Millard <marklmi@yahoo.com> To: FreeBSD PowerPC ML <freebsd-ppc@freebsd.org>, Justin Hibbits <chmeeedalf@gmail.com> Subject: Looks like ap_letgo use needs platform specific code to allow avoiding the "sleep-gets-stuck" problem on PowerMac11,2's . . . Message-ID: <B5B1CC39-1D75-42F4-9661-62DA9D029D34@yahoo.com>
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[Note: My context is tied to getting usefdt mode operable on
old PowerMacs. The below is only tested for usefdt mode
so far.]
The following investigatory patch has so-far stopped my having
sleep-gets-stuck problems (only seen on 2-socket/1-core-each
970 MP G5 Powermac11,2's as far as I know):
# svnlite diff /usr/src/sys/powerpc/powerpc/mp_machdep.c | more =
=
Index: =
/usr/src/sys/powerpc/powerpc/mp_machdep.c
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
--- /usr/src/sys/powerpc/powerpc/mp_machdep.c (revision 345758)
+++ /usr/src/sys/powerpc/powerpc/mp_machdep.c (working copy)
@@ -77,9 +77,10 @@
PCPU_SET(awake, 1);
__asm __volatile("msync; isync");
=20
+ powerpc_sync();
while (ap_letgo =3D=3D 0)
- __asm __volatile("or 31,31,31");
- __asm __volatile("or 6,6,6");
+ powerpc_sync();
+ isync();
=20
/*
* Set timebase as soon as possible to meet an implicit =
rendezvous
@@ -262,8 +263,11 @@
__asm __volatile("msync; isync");
=20
/* Let APs continue */
- atomic_store_rel_int(&ap_letgo, 1);
+ ap_letgo=3D 1; // depend on prior sync, no need to lwsync =
first
=20
+ powerpc_sync(); // analogous to what the ap's do (more similar =
time frame?)
+ if (ap_letgo) isync();
+
platform_smp_timebase_sync(ap_timebase, 0);
=20
while (ap_awake < smp_cpus)
Apparently, the use of "or 31,31,31" causes sizable
variations in the time frame when the platform_smp_timebase_sync
happens on the various cores across the two 970MPs.
It looks something like a platform_ap_letgo_wait is appropriate,
with a powermac_ap_letgo_wait specific one, say. (Or, possibly,
AIM specific but spanning powermac?)
The above patch has booted and operated the 2-socket PowerMac7,2
context fine as well so far. I'll check the G5's and a G4
dual-socket with a 32-bit powerpc build.
I've no clue if there are any time-mismatch issues across
sockets/cores/hw-threads for the "8-way SMT" contexts with
"dozens to hundreds of CPUs".
I've only been testing for part of today and I do not have
access to any non-PowerMac PowerPC contexts. So this is
preliminary but I do not expect "or 31,31,31" is going to
be appropriate to the PowerMac11,2 contexts that caused
my investigation of the issue.
=3D=3D=3D
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)
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